Step 2: LEDs Soldered to Aluminum Base Plate

Most 3W LEDs are soldered to 1-LED base plates. To save space on the heatsink and simplify wiring, solder the emitters to a 4-LED aluminum base plate with thermal paste on their cooling surfaces. For a 12V power supply, each base plate can have up to 3 blue LEDs or 4 red LEDs. The LEDs from the beads must be desoldered from their original base plates before soldering them to 4-LED base plates.

Step 3: Heatsink Marked for Drilling

Mark the heatsink for mounting its parts and indent the marking with center punch. I used an aluminum CD rack as the heatsink.

The tap and drill bit sizes are:

3mm and 2.5mm for the LEDs and circuit board

#6-32 and #36 for the fans, stands, and air deflectors

Step 4: Heatsink Drilled and Tapped for Fans

Step 5: Heatsink Drilled and Tapped for LEDs

For maximum heat conduction, the base plates should be positioned so that the LEDs are directly above the heatsink's flat surfaces. The screw sizes for the LEDs should be M3 x 10mm. Nylon washers are used to prevent shorting and the split ring washers keep the screws tightened.

Step 6: Heatsink Drilled for Cable Ties

The cable ties will be used to hold the LED's wiring.

Step 7: Heatsink Drilled and Tapped for LED Driver

To keep the wires short, I mounted the circuit board on the heatsink. Nylon standoffs were used because they are non-conductive.

Step 8: Heatsink Drilled and Tapped for Stands

The LEDs are delicate so the four #6-32 x 2" screws serve as a stand to protect them while you are working on this project.

Step 9: Heatsink Drilled and Tapped for Air Deflectors

The air deflectors increase the airflow through the heatsink. You can use them if the heatsink is too hot or more LEDs are used.

Step 10: PC Chassis Drilled for Mounting and Ventillation

Step 11: LED Driver Circuit

In this circuit, LED drivers were used for four strings of deep red LEDs and four strings of royal blue LEDs which were the wavelengths growing plants. Only two strings were shown to simplify the diagram. SW3 controls the blue LEDs and SW4 controls the red LEDs which uses the +12V rails. The current limit is around 15A. Some PSU's even have dual +12V rails for higher output! The +5Vsb rail is on during standby and allows the green LED to be used at night. Plants do not detect green light as
daytime and is less dazzling for viewing your plants. All three wavelengths of LEDs have their
own fuses.

An external 5V source can be plugged in to a 2-prong lamp timer to control daylight hours. Some plants depend on daylight hours for flowering. Turning on SW2 or supplying 5V through the DC jack turns on Q1 which shorts PG-ON to ground.

In the zip file, I have included the ExpressPCB files with a printable sample for the stripboard.

Attachments

Step 12: Stripboard Track Cutting

Step 13: Soldered LED Driver Circuit Board

For the strip board sample, I used green lines for the wire connections, red lines for the copper cladding strips, red circles for the stand-offs, and red squares for the track cuttings. To solder the ATX connector which has 18AWG wires, the mounting holes need to be enlarged by drilling. SW1 and the DC power jack will be screwed to the case.

Step 14: Soldering the LEDs

Step 15: LED Base Plates With Thermal Plaster

Step 16: Hot Glue As Wire Strain Relief

Step 17: Rewiring the ATX Power Supply

You will need the wires +5Vsb (purple), +12V (yellow), 0v (black), 3.3V (orange), 3.3V sense (thin orange or brown), and PG-ON (green). You should keep two or three sets of connectors to power more grow light units in the future. The remaining wires can be clipped. The 3.3V wire must be connected to its voltage sense wire.

Modify a four pin connector so that:

One black wire is connected to PG-ON

One black wire is connected to 0V

One red wire is connected to +5vsb (not +5V)

One yellow wire is connected to +12V

For the expansion connectors, you only need the +12V and 0V rails.

Step 18: Rubber Washers for Spacing the Fan

To keep the fan from touching the chassis while running, space it with 4 washers. Use #6-32 x 2 1/2" screws for the fan. It will be used for attaching the grow light to the chassis. With only one 120mm fan, the heatsink did not get too hot.

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6 Comments

once again, i really like your work hanlin. this is an amazing post, and the addition of the green light is just brilliant. i'm updating my system, working on a light system similar to yours, i will post my work once done.. thank you for sharing !!

So you have 29 x 3 Watt LEDs it seems, so what max. power is 29 x 3 = 87 Watts right? But what Amperage are you running it at to get the actual draw, might be like 60% of that so you don;t burn them out right? I am keen to see if I can improve on this awesome design, it is a good place for me to start. They do sell PC grow boxes it seems with LEDs so you are on to a good thing.

What spectrum does this set up cover, are 'white' LEDs something that could be useful or does your mix of red/blue and a green cover this nicely?